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From: Olivier Leprêtre <o.lepretre@gmail.com>
To: pgsql-sql@lists.postgresql.org
Subject: RE: nth_value and row_number in a partition
Date: Thu, 25 Jan 2018 20:49:25 +0100
Message-ID: <016401d39615$9b620bd0$d2262370$@gmail.com> (raw)
In-Reply-To: <CAKFQuwa3SCRhpnjOK0=dNxL=vt2Lvrs9VYLhJ8p2UZrUqieShQ@mail.gmail.com>
References: <015201d3960a$a2db0b60$e8912220$@gmail.com>
	<CAKFQuwa3SCRhpnjOK0=dNxL=vt2Lvrs9VYLhJ8p2UZrUqieShQ@mail.gmail.com>

Hi David,

 

Thanks for your answer, I tried your suggestion as well as many other combinations, no success. Here are some of them. I just don't understand which syntax is required

 

select roads,orders,(first_value(v1) 

over (partition by roads,segment order by orders)-(nth_value(v2,cast(row_number() over (partition by roads,order by orders)  as integer)) over (partition by roads,segment order by orders))) as result 

from mytable

or

select roads,orders,(first_value(v1) 

over (partition by roads,segment order by orders)-(nth_value(v2,row_number() over (partition by roads,order by orders)::integer)) over (partition by roads,segment order by orders))) as result 

from mytable

 

>>syntax error near order (bold)

 

select roads,orders,(first_value(v1) 

over (partition by roads,segment order by orders)-(nth_value(v2,row_number() over (partition by roads)::integer)) over (partition by roads,segment order by orders))) as result 

from mytable

 

>> syntax error near over

 

select roads,orders,(first_value(v1) 

over (partition by roads,segment order by orders)-nth_value(v2,row_number() over (partition by roads)::integer) over (partition by roads,segment order by orders)) as result 

from mytable

 

>> window call cannot be imbricated

 

select roads,orders,(first_value(v1) 

over (partition by roads,segment order by orders)-nth_value(v2,row_number()  over (partition by roads,segment order by orders)::integer)) as result 

from mytable

 

>> nth_value requires an over clause

 

select roads,orders,(first_value(v1) 

over (partition by roads,segment order by orders)-nth_value(v2,row_number()::integer) over (partition by roads,segment order by orders)) as result 

from mytable

 

>> row_number requires an over clause

 

 

 

 

 

De : David G. Johnston [mailto:david.g.johnston@gmail.com] 
Envoyé : jeudi 25 janvier 2018 19:44
À : Olivier Leprêtre <o.lepretre@gmail.com>
Cc : pgsql-sql@lists.postgresql.org
Objet : Re: nth_value and row_number in a partition

 

On Thursday, January 25, 2018, Olivier Leprêtre <o.lepretre@gmail.com <mailto:o.lepretre@gmail.com> > wrote:

nth_value(integer, bigint) doesn't exists.  

This is close, you just need to cast to integer. 

(cast(row_number() as integer)  over (partition by roads,segments order by orders))) 

You cannot separate the window function from its over clause.

 

Cast( Row_number() over (...) as integer )

 

Not tested...and I tend to use :: instead of cast

 

David J.

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